Gister-CL can be used to help automate the above process. In practice,
it may not be possible to know and assess characteristics of even
friendly, much less enemy, forces. For example, assessing
characteristics like morale, readiness, and tradition is a highly
subjective process. Thus, it may be difficult to give a precise FM
value, so a range is given instead. Furthermore, one may be uncertain
about any assessment of a FM they might wish to express. Consequently,
evidential reasoning is important for selecting an appropriate unit.

Unit selection involves first comparing the perceived strength of
friendly and potential enemy forces, then selecting a unit based on
the degree to which a unit meets or exceeds prespecified
strength-ratio requirements. Accomplishing this within an ER
framework requires constructing frames of discernment and
relationships between them for both friendly and enemy unit forces. A
frame is constructed that represents the nominal ``base'' strength for
each unit, and other constructed frames represent the FM assessments
of other force characteristics. Within Gister-CL, these frames are
constructed in a gallery as shown in
Figure 2. Frames corresponding to a
friendly force begin with ``F", and frames corresponding to an enemy
force begin with an ``E".

Figure 2: Gister gallery for Army unit selection

Relationships between the frames are represented by connecting arcs
called compatibility relations (CRs), which compute the result
of combining frames. In our example, CRs are often
multiplicative. However, some are not. For example,
the relative firepower of a unit depends on the relative values of its constituent
TROOPS and ARMAMENT FM values. The RELATIVE FIREPOWER FM value is, in our
implementation, the maximum as opposed to the product of the FM values in the TROOPS
and ARMAMENT frames. The reason for this dependence is that even if a unit does not
have its full complement of troops, the remaining troops may have sufficient
armament to balance deficiencies in troops. Conversely, a unit may have sufficient
troops to balance deficiencies in armament.

Figure 3: Result of degree to which unit meets force ratio
requirements.

Given a set of FMs for a subset of friendly and enemy characteristics,
a Gister-CL analysis is used to reason about the characteristics and
come to a conclusion about each unit. For example, an analysis of the
characteristics of a particular unit for a deterrent mission against
a particular enemy force results in the distribution shown in
Figure 3.